Geant4 Monte Carlo simulation study of the secondary radiation fields at the laser-driven ion source LION

M Tisi,J Schreiber,F S Englbrecht,V Mares,W Rühm

doi:10.1038/s41598-021-03897-2

Abstract

At the Center for Advanced Laser Applications (CALA), Garching, Germany, the LION (Laser-driven ION Acceleration) experiment is being commissioned, aiming at the production of laser-driven bunches of protons and light ions with multi-MeV energies and repetition frequency up to 1 Hz. A Geant4 Monte Carlo-based study of the secondary neutron and photon fields expected during LION’s different commissioning phases is presented. Goal of this study is the characterization of the secondary radiation environment present inside and outside the LION cave. Three different primary proton spectra, taken from experimental results reported in the literature and representative of three different future stages of the LION’s commissioning path are used. Together with protons, also electrons are emitted through laser-target interaction and are also responsible for the production of secondary radiation. For the electron component of the three source terms, a simplified exponential model is used. Moreover, in order to reduce the simulation complexity, a two-components simplified geometrical model of proton and electron sources is proposed. It has been found that the radiation environment inside the experimental cave is either dominated by photons or neutrons depending on the position in the room and the source term used. The higher the intensity of the source, the higher the neutron contribution to the total dose for all scored positions. Maximum neutron and photon ambient dose equivalent values normalized to 109 simulated incident primaries were calculated at the exit of the vacuum chamber, where values of about 85 nSv (109 primaries)−1 and 1.0 μSv (109 primaries)−1 were found.

Highlights

Thanks to the recent improvements in laser peak power, energy density, laser temporal contrast and to the large investigation of suitable target materials, in the last two decades, several groups achieved the acceleration of protons and light ions up to an energy of several tens of M eV1
LION employs ATLAS3000, a Ti:Sapphire-based laser, whose main properties are summarized in Table 1, and as targets, 0.01–1 μm thick metal or carbon-based samples mounted on a rotating sample holder[5]
The ultimate goal pursued at LION is the exploitation of the Target Normal Sheath Acceleration (TNSA) and Radiation Pressure Acceleration (RPA) regimes, in order to realize a laser-driven ion source with the capability to deliver collimated bunches of several tens of MeV ions at 1 Hz repetition frequency to serve as a facility for radiation therapy r esearch[6]

Summary

Introduction

Thanks to the recent improvements in laser peak power, energy density, laser temporal contrast and to the large investigation of suitable target materials, in the last two decades, several groups achieved the acceleration of protons and light ions up to an energy of several tens of M eV1. The ultimate goal pursued at LION is the exploitation of the Target Normal Sheath Acceleration (TNSA) and Radiation Pressure Acceleration (RPA) regimes, in order to realize a laser-driven ion source with the capability to deliver collimated bunches of several tens of MeV ions (protons and carbon ions) at 1 Hz repetition frequency to serve as a facility for radiation therapy r esearch[6]. At the current status of the facility’s commissioning (2020), ATLAS3000 is delivering to LION laser pulses with energy up to 10 J. Shot on demand energetic ions, detected above the background noise) and charge per bunch that are lower to those expected at full operation

Methods

Results

Discussion

Conclusion